Conventionally, X-ray computed tomography is generally performed while a patient is lying on a bed in a prone position. On the other hand, demands have arisen for an X-ray computed tomography for an object in a standing position.
When executing such computed tomography, a conventionally used X-ray computed tomography (CT) apparatus is tilted through 90°. At this time, when an object falls outside an imaging range, the acquired image cannot be used for diagnosis, resulting in unnecessary exposure to radiation.
When the gantry body of an X-ray CT apparatus placed in a horizontal position is lowered from the ceiling side, in order to check in advance whether the gantry body interferes with an object, chair-like bed, or the like, prevention apparatus which applies downward an interference examination light beam having a circumferential irradiation range having a predetermined radius smaller than the radius of an examination hole (gantry opening) into which the object is inserted.
In this case, if the predetermined radius is set to be equal to that of the imaging range by using the interference prevention apparatus in order to prevent unnecessary exposure to radiation, even when a portion other than the imaging area falls outside the imaging range, it is necessary to take measures such as stopping an imaging operation. This leads to prolongation of the imaging time.